Step 1: Introduction to Gemology

Lesson 2

For thousands of years, terms such as rubies, sapphires, gems, and jewels have been in our vocabulary. However, some find defining a gem quite challenging. Not everyday people with common sense but people like lexicographers, who need to define each word in our language very precisely. I feel sorry for them, since simply no concise definition covers all the materials that have been regarded as gemstones throughout the centuries.

A Working Definition of a Gem?

The following definition covers the vast majority of the stones we regard as gems:

Minerals that have been chosen for their beauty and durability, then cut and polished for use as human adornment.

Still, every defining feature in that definition has exceptions. This creates problems.

Minerals vs. Organics

Most gems are minerals, but some, notably pearl and amber, are organics. Living organisms create these materials. By definition, a mineral must be created inside the earth. (To add some confusion, a pearl’s coating is a mineral though it’s created in a mollusk). Hence, pearls fall into a different category. Likewise, amber began life as tree sap. After millions of years, it transformed into a polymer, a natural plastic. People have regarded amber as a gem for thousands of years, although it’s definitely not a mineral.


Some people would consider gems colored Pepto Bismol pink and olive green (like unakite) unattractive. Some find them beautiful. Brown gems enjoy some popularity in “earth tone” jewelry pieces. Of course, others have different tastes. Beauty may be in the eye of the beholder, but do all who choose gems choose beauty? Do all gem enthusiasts select gemstones because they find them beautiful?

gem definitions - unakite

“Green Brooch with Fabric Trim,” unakite with Japanese seed beads, by Medusa Jewellery. Licensed under CC By-ND 2.0.


For gemstone buyers, durability or wearability is usually a high priority. Nevertheless, two of the most popular gems are particularly delicate. Pearls generally last about a century as jewelry stones due to their softness. The simple act of wiping off dust will slowly wear away their coating. Perfumes and hairsprays can also stain and damage pearls.

Highly valued throughout history, opals are notoriously delicate. As they lose their high water content, they dry out and may crack. They may break with the slightest bump. They’re heat sensitive, too. I knew one customer who had a prized opal brooch in a protective setting. One night, as she left a Christmas party, the opal shattered with an audible crack as she went from the warmth indoors to the cold winter night. Many have shed tears over opals.

Cutting and Polishing

So much for beauty and durability. How about cutting and polishing? Currently, many people love using whole crystals in jewelry. In decades past, this wasn’t the case. Mother Nature’s crystals can be exceptionally beautiful. Some even believe they have special metaphysical properties that are enhanced when left whole. So, we can’t insist that our gems be cut and polished, either.


The last qualification usually associated with a gemstone is its use for human adornment. People have cut, polished, and admired about 3,000 minerals. Of these, only about a hundred show up in jewelry. The rest are simply too delicate to wear well. They fall strictly in the collector’s domain.

gem definitions - cinnabar

“Cinnabar with Quartz,” Almaden, Almaden District, Ciudad Real, Castile-La Mancha, Spain. ? Rob Lavinsky, Used with permission.

Not Quite Scientific, but…

Gemology was only first recognized as a science in the 1930s. Until that time, people considered all transparent, red gems rubies, blue ones sapphires, and green ones emeralds. Today, as a professional, I can only call a crystallized beryllium-aluminum silicate with trace amounts of chromium an emerald. Other beautiful green gems could be tsavorite, tourmaline, and diopside.

The allure of gemstones lies in their fantasy of color and light. Beautifully colored stones have intrigued people since time immemorial. The love of gems hasn’t changed. However, we now have to contend with a very scientific element. As much as I love the science of gemology, it has the unfortunate side effect of taking much of the mystique and romance out of our stones.

To heck with the definitions. If it makes your eyes light up, it’s a true gem!

gem definitions - diopside

“Diopside, Calcite,” Aliabad, Hunza Valley, Gilgit District, Gilgit-Baltistan (Northern Areas), Pakistan, by Géry Parent. Licensed under CC By-ND 2.0.